Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guidewire, possibly in combination with other intravascular devices such as stents. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guidewire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures including fixed-wire (FW) catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art. An example of an OTW catheter may be found in commonly assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly assigned U.S. Pat. No. 5,156,594 to Keith.
Manufacturers are constantly in search of materials and designs that enhance the performance of their intravascular catheters. One particular source of improvement has been the incorporation of performance enhancing polymeric materials into their intravascular catheter designs. Certain polymeric materials enable the catheter to be more lubricious, thereby aiding the advancement of a guidewire within the body of the catheter. Other polymeric materials make particular sections of the catheter more rigid, thereby aiding the catheter in its advancement through the patient's anatomy. The primary drawback to using specialized polymeric materials is that often the individual polymers forming the structural components are incompatible with one another. This is a particular problem for manufacturers who must combine the individual components to form a single operable intravascular catheter.
One solution to the use of incompatible polymers has been to place a layer between the two incompatible polymeric structural components that is sufficiently bondable to either component. In effect, this distinct layer “ties” the two structural components together, thereby receiving its commonly referred to name as a tie layer. Tie layers have been extruded over the length of intravascular catheters. This added layer, regardless of its thickness, affects the performance characteristics of an intravascular catheter shaft incorporating the tie layer.
Several performance characteristics that are important to intravascular catheters include pushability, trackability and crossability. Pushability refers to the catheter's ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the catheter's ability to navigate tortuous vasculature. Crossability refers to the catheter's ability to navigate the balloon catheter across narrow restrictions in the vasculature, such as stenosed vessels or fully and partially deployed stents. All of the above performance characteristics are interrelated and depend on the design of the catheter shaft over its length.
It is a manufacturing goal to reduce the profile of a manufactured intravascular catheter. A reduced profile catheter is less likely to positively engage the surrounding vascular walls. Additionally, a reduced profile catheter is also more likely to cross and re-cross over a stenosed region or a deployed stent.